A pilot system integrating a settling technique and a horizontal subsurface flow constructed wetland for the treatment of polluted lake water.

An integrated system was tested at pilot-scale for treating polluted water from the Marriot Lake in Egypt, comprising a settling technique followed by three parallel horizontal subsurface flow constructed wetland (HFCWs) units operating under a continuous flow mode; one HFCW unit was planted with Typha angustifolia and contained a perforated pipes network for enhanced passive aeration (CWA), one unit was planted without the perforated pipe network (CWR) and one served as a Control unit (unplanted and without perforated pipes). Changes in physicochemical parameters, BOD5, nutrients (nitrogen, phosphorus), microbial community, and trace metals at different hydraulic retention times (HRT; 0.5-6 h) and hydraulic loading rates (HLR; 750, 1000, 1250, and 2000 L/m2/d) were monitored. The CWA unit had an overall better performance than the CWR unit, while both planted units outperformed the Control unit. CWA showed the highest performance at HLR of 1000 L/m2/d and 4-6 h-HRT with 95.3% removal for turbidity, 83% for BOD5, 99.3% for ammonia nitrogen (NH4-N), 70.8% for Total Nitrogen (TN), and 66.7% for Total Phosphorus (TP), while higher NO3-N and NO2-N effluent concentrations were observed. Trace metals levels were significantly reduced and accumulated in plant tissues. Microbial communities' densities fluctuated in the CWA unit. The integrated system with the settling stage and the planted CWA unit was proved to achieve a high removal efficiency and reached the national discharge limits, thus representing a novel nature-based solution for the sustainable remediation of polluted lake water.

Internalisation of Salmonella spp. by Typha latifolia and Cyperus papyrus in vitro and implications for pathogen removal in Constructed Wetlands.

ABSTRACTFreshwater contamination by enteric pathogens is implicated in the high frequency of diarrhoeal diseases in low to middle income countries, typically due to poor wastewater management. Constructed Wetlands are a cost-effective and sustainable alternative to conventional/mechanical treatment technologies, but the pathogen removal mechanisms in Constructed Wetlands are not fully understood. This study investigated for the first time the internalisation of Salmonella spp. by Typha latifolia and Cyperus papyrus in hydroponic microcosms. Presence of Salmonella spp. within roots, rhizomes and shoots was assayed using agar-based methods over a period of 12 days. Concentration of Salmonella spp. in growth media showed 2.7 and 4.8 log unit reduction with T. latifolia and C. papyrus, respectively, and 1.8 and 6.0 log unit in unplanted units. Salmonella spp. was recovered from root and rhizome tissues of T. latifolia (up to 4.4 logCFU/g) and C. papyrus (up to 3.4 logCFU/g), and the bacteria were highly concentrated in the epidermis and cortex. However, Salmonella spp. was not detected in the stems and leaves of the two plant species. The present study demonstrates for the first time that these macrophytes internalise cells of Salmonella spp., which could be one pathogen removal mechanism employed by wetland plants.

Green Roofs Towards Circular and Resilient Cities.

Green roofs are gaining interest as nature-based solutions (NBS) to counteract with several environmental and socio-economic problems associated to urban sprawl and climate change. The challenge is to transform the built environment through the inclusion of NBS. Taking advantage of the existing space in the top of the buildings, the integration of green roofs will support the cities' transition towards circularity and resilience. They provide several ecosystem services and can act as multifunctional and decentralized units. In order to boost these services, green roofs need to be effectively incorporated and replicated in the urban landscape. Different configuration of systems may be considered depending on the challenges that the city foresees. To fully implement green roofs, it is important that (i) barriers are identified and overcome, (ii) standardization is set to grant liability, (iii) policies, incentives, and strategies are properly established, (iv) organizations delivering NBS services are leveraged, and (v) awareness and dissemination promotion, as investment in education, are considered. This paper intends to give an overview of the importance of green roof integration in the urban environment considering the dimensions of the building and the city, having underlined their contribution to circularity and cities' resilience.

Hydraulic characterization and removal of metals and nutrients in an aerated horizontal subsurface flow "racetrack" wetland treating primary-treated oil industry effluent.

Constructed wetlands (CW) are an attractive technology due to their operational simplicity and low life-cycle cost. It has been applied for refinery effluent treatment but mostly single-stage designs (e.g., vertical or horizontal flow) have been tested. However, to achieve a good treatment efficiency for industrial effluents, different treatment conditions (both aerobic and anaerobic) are needed. This means that hybrid CW systems are typically required with a respectively increased area demand. In addition, a strong aerobic environment that facilitates the formation of iron, manganese, zinc and aluminum precipitates cannot be established with passive wetland systems, while the role of these oxyhydroxide compounds in the further co-precipitation and removal of heavy metals such as copper, nickel, lead, and chromium that can simplify the overall treatment of industrial wastewaters is poorly understood in CW. Therefore, this study tests for the first time an innovative CW design that combines an artificially aerated section with a non-aerated section in a single unit applied for oil refinery wastewater treatment. Four pilot units were tested with different design (i.e., planted/unplanted, aerated/non-aerated) and operational (two different hydraulic loading rates) characteristics to estimate the role of plants and artificial aeration and to identify the optimum design configuration. The pilot units received a primary refinery effluent, i.e., after passing through a dissolved air flotation unit. The first-order removal of heavy metals under aerobic conditions is evaluated, along with the removal of phenols and nutrients. High removal rates for Fe (96-98%), Mn (38-81%), Al (49-73%), and Zn (99-100%) generally as oxyhydroxide precipitates were found, while removal of Cu (61-80%), Ni (70-85%), Pb (96-99%) and Cr (60-92%) under aerobic conditions was also observed, likely through co-precipitation. Complete phenols and ammonia nitrogen removal was also found. The first-order rate coefficient (k) calculated from the collected data demonstrates that the tested CW represents an advanced wetland design reaching higher removal rates at a smaller area demand than the common CW systems.

Effect of design and operational parameters on nutrients and heavy metal removal in pilot floating treatment wetlands with Eichhornia Crassipes treating polluted lake water.

Though having an economic and ecological impact on Marriott Lake management in Egypt, water hyacinth (Eichhornia crassipes) is an aquatic floating macrophyte with a known phytoremediation potential. In order to assess its remediation potential, pilot floating treatment wetlands (FTWs) with E. crassipes were built in duplicates to evaluate the removal of nutrients and heavy metals from the polluted lake water. The experimental design included units with different water depths (15, 25, and 35 cm; D15, D25, and D35, respectively) and plant coverage (90, 70, 50, and 0%; P90, P70, P50, and P0, respectively). The pilot FTWs were monitored over a 7-day operation cycle to identify the optimum combination of design (plant coverage, water depth) and operation (hydraulic retention time; HRT) parameters needed for maximum BOD5, TN, NH4-N, and TP removal. NH4-N removal reached 97.4% in the D25P50 unit after 3 days, BOD5 75% in the D15P90 after 3 days, TN 82% in the D25P70 after 4 days, and TP 84.2% in the D35P70 after 4 days. The open-water evaporation rate was higher than the evapotranspiration rate in the planted units, probably due to the warm climate of the study area. Metals were also sufficiently removed through bioaccumulation in plant tissues in the order of Fe > Pb > Cu > Ni (62.5%, 88.9%, 81.7%, and 80.4% for D25P50, D25P70, D25P50, and D25P90, respectively), while most of the assimilated metal mass was translocated to the plant roots. The biochemical composition of the plant tissue was significantly different between the shoot and root parts. Overall, the FTW with 70% E. crassipes coverage, 25-cm water depth, and an HRT of 3-5 days was identified as the optimum design for effective remediation of the polluted Marriott Lake in Egypt.

Treatment of cork boiling wastewater using a horizontal subsurface flow constructed wetland combined with ozonation.

Cork boiling wastewaters (CBW) are strongly coloured complex aqueous solutions with high organic load of biorecalcitrant and toxic nature. The feasibility and efficiency of a CBW treatment process combining ozonation as pre- and post-treatment of a horizontal subsurface flow constructed wetland (HSFCW) was assessed. Over an extended monitoring period of 390 days, two lab-scale HSFCW units were tested; one planted with P. australis (CWP) and one unplanted-control (CWC) operated at average organic loads rates (OLR) of 5 and 10 g COD/m2/d. CWP always outperformed the control unit. The ozonation trials were run at pH values of 8.15-8.21 and 5.39-5.45 (without adjustment) at ozone to COD ratios of 0.25-0.29 and 0.24-0.59 when implemented as pre- and post-treatment, respectively. Average removals (calculated through mass balance basis) were 78-88%, 86-91%, 71-89% and 43-89% for COD, BOD5, Total Phenols (TPh) and colour when ozonation was implemented as post-treatment. For ozonation as pre-treatment, respective figures were 77-80%, 79-92%, 78-85% and 19-73%. Regardless of the treatment scheme and OLR, ozonation was very effective in biodegradability increase (i.e., BOD5/COD) from 0.18 to 0.42 when applied as pre-treatment, and decolourization after the HSFCW increased from 21% to 91% (post-treatment) with respective ozone consumed yields of 67-69% and 72-85%. The best results were obtained for the scheme CWP + Ozonation at OLR of 5.33 g COD/m2/d with COD reductions from 1950 mg/L to 81-88 mg/L in the effluent and TPh from 125 mg/L to 5-6 mg/L at limited ozone amounts of 0.21-0.45 g O3/m2/d.

A novel pilot and full-scale constructed wetland study for glass industry wastewater treatment.

Industrial wastewaters represent a serious threat to the environment due to their variable and complex composition. Though mostly mechanical systems are used for treatment of such wastewater, there is growing need for sustainable and cost-effective solutions, especially in low-income regions. In this study, a horizontal sub-surface flow Constructed Wetland (HSFCW) system was used for the first time to treat wastewater from a glass manufacturing industry in Iran. In order to de-risk the treatment approach, a pilot system consisting of a settling tank and a HSFCW was first tested for 4 months. The results of the pilot study were then used to build the full-scale CW system treating 10 m³/day. In general, the tested design proved to be very effective reaching high removal rates of BOD5, COD, and TSS (90, 90, and 99, respectively), as also for TN and TP (>90%). The high efficiency of the tested system allowed for the recycle and reuse of the treated effluent in the glass manufacturing processes, reducing this way the fresh water consumption in the glass industry and the related operational costs.

Investigation of pilot-scale constructed wetlands treating simulated pre-treated tannery wastewater under tropical climate.

Tannery wastewater is characterized by high and variable concentrations of diverse pollutants, which makes it difficult and costly to treat. In the search for sustainable treatment options for tannery effluents, two pilot-scale horizontal subsurface flow (HSF) constructed wetlands (CW) were built and operated for the treatment of synthetic water of quality similar to that of pre-treated tannery effluents. Five different loading phases were examined with gradual increase of inflow COD, NH4+-N and Cr loads until reaching and exceeding the typical composition of a tannery effluent. High COD and NH4+-N removals were observed (82 and 96%, respectively), and almost complete Cr removal in the outflow, which met the Venezuela national standards for environmental discharge. Plant uptake was measured, but microbial processes appear to be the main ammonium transformation/removal mechanism. Nitrogen, chlorophyll and Cr in the plant aerial parts and roots indicated the capacity of Phragmites sp. to grow and survive even under high loads. The measured heterotrophic bacteria in the substrate and rhizomes indicated the biofilm development and the oxidation of organic matter and nitrogen. Water losses via evapotraspiration were also measured and reached 14%. Overall, the tested CW design proved to be a sustainable and feasible alternative for the treatment of tannery wastewater in tropical climates.

Investigation of lab-scale horizontal subsurface flow constructed wetlands treating industrial cork boiling wastewater.

The feasibility and treatment efficiency of horizontal subsurface flow constructed wetlands (HSFCW) was assessed for the first time for cork boiling wastewater (CBW) through laboratory experiments. CBW is known for its high content of phenolic compounds, complex composition of biorecalcitrant and toxic nature. Two lab-scale units, one planted with Phragmites australis (CWP) and one unplanted (CWC), were used to evaluate the removals of COD, BOD, total phenolic compounds (TPh) and decolourization over a 2.5-years monitoring period under Mediterranean climatic conditions. Seven organic and hydraulic loading rates ranging from 2.6 to 11.5 g COD/m2/d and 5.7-9.1 L/m2/d were tested under average hydraulic retention time (HRT) of 5 ±â€¯1 days required due to the CWB limited biodegradability (i.e., BOD5/COD of 0.19). Average removals of the CWP exceeded those of the CWC and reached 74.6%, 91.7% and 69.1% for COD, BOD5 and TPh, respectively, with respective mass removals rates up to 7.0, 1.7 and 0.5 (in g/m2/d). Decolourization was limited to 35%, since it mainly depends on physical processes rather than biodegradation. CBW concentration of nine phenolic compounds ranged from 1.2 to 38.4 mg/L (for the syringic and ellagic acids, respectively) in the raw CBW, with respective removals in the CWP unit ranging from 41.8 to 76.3%, higher than those in the control unit. Despite CBW high concentration of TPhs (average of 116.3 mg/L), the HSFCW reached organic load removals higher than those of conventional biological treatment methods.

A novel horizontal subsurface flow constructed wetland: Reducing area requirements and clogging risk.

The use of Constructed Wetlands (CWs) has been nowadays expanded from municipal to industrial and agro-industrial wastewaters. The main limitations of CWs remain the relatively high area requirements compared to mechanical treatment technologies and the potential occurrence of the clogging phenomenon. This study presents the findings of an innovative CW design where novel materials were used. Four pilot-scale CW units were designed, built and operated for two years. Each unit consisted of two compartments, the first of which (two thirds of the total unit length) contained either fine gravel (in two units) or random type high density polyethylene (HDPE) (in the other two units). This plastic media type was tested in a CW system for the first time. The second compartment of all four units contained natural zeolite. Two units (one with fine gravel and one with HDPE) were planted with common reeds, while the other two were kept unplanted. Second cheese whey was introduced into the units, which were operated under hydraulic residence times (HRT) of 2 and 4 days. After a two-year operation and monitoring period, pollutant removal rates were approximately 80%, 75% and 90% for COD, ammonium and ortho-phosphate, respectively, while temperature and HRT had no significant effect on pollutant removal. CWs containing the plastic media achieved the same removal rates as those containing gravel, despite receiving three times higher hydraulic surface loads (0.08 m/d) and four times higher organic surface loads (620 g/m2/d). This reveals that the use of HDPE plastic media could reduce CW surface area requirements by 75%.

Removal of dimethylphenols and ammonium in laboratory-scale horizontal subsurface flow constructed wetlands.

Phenolic compounds in industrial wastewaters are toxic pollutants and pose a threat to public health and ecosystems. More recently, focus is being directed toward combining the treatment of these compounds with a cost-effective and environmentally sound technology. The removal efficiency of dimethylphenol and ammonium nitrogen was studied, for the first time, in three different laboratory-scale horizontal subsurface flow constructed wetlands planted with Juncus effusus. Two of the wetlands used were filled with gravel. One of these was planted and the second left without vegetation. The third wetland was a hydroponic system. It was found that the removal efficiencies of dimethylphenol was dependent on the inflow loading of the contaminant and was higher in the planted systems. Both planted systems yielded 99% removal efficiency up to loads of 240 mg/d, compared to only 73% for the unplanted constructed wetland. Factors and processes such as redox dynamics, methanogenesis, reduction of ammonium and low nitrate and nitrite concentrations imply simultaneous aerobic and anaerobic dimethylphenol transformations. A significant surplus of organic carbon was detected in the planted wetlands, which may originate from intermediates of the dimethylphenol transformation processes and/or organic plant root exudates. The present study demonstrates that horizontal subsurface flow constructed wetlands are a promising alternative system for the treatment of effluents contaminated with dimethylphenol isomers.

Heavy metal fate in pilot-scale sludge drying reed beds under various design and operation conditions.

Thirteen pilot-scale sludge drying reed bed (SDRB) units have been constructed and operated under various settings. The beds included a cobbles lower layer, where perforated PVC aeration tubes were placed, and two gravel layers on top. The setup included planted beds with common reeds and control units. Three sludge loading rates (SLR) were examined: 30, 60 and 75 kg dm/m(2)/yr. Heavy metal (HM) accumulation in the residual sludge layer was negligible or low, and was found to increase with sludge layer depth. Plant uptake was low; the belowground biomass accumulated significantly more HMs compared to the aboveground biomass. Less than 16% of the influent HM left the bed through drainage. HM accumulation in the gravel layer was the major metal sink in the mass balance. On the whole, the HM content of the residual sludge was below the legal limits proposed by the EU for land application.

Stability and maturity of thickened wastewater sludge treated in pilot-scale sludge treatment wetlands.

Thickened wastewater activated sludge was treated in 13 pilot-scale sludge treatment wetlands of various configurations that operated continuously for three years in North Greece. Sludge was loaded for approximately 2.5 years, and the beds were left to rest for the remaining period. Three different sludge loading rates were used that represented three different population equivalents. Residual sludge stability and maturity were monitored for the last year. Sludge was regularly sampled and microbial respiration activity indices were measured via a static respiration assay. The phytotoxicity of sludge was quantified via a seed germination bioassay. Measurements of total solids, organic matter, total coliforms, pH and electrical conductivity were also made. According to microbial respiration activity measurements, the sludge end-product was classified as stable. The germination index of the final product exceeded 100% in most wetland units, while final pH values were approximately 6.5. The presence of plants positively affected the stability and maturity of the residual sludge end-product. Passive aeration did not significantly affect the quality of the residual sludge, while the addition of chromium at high concentrations hindered the sludge decomposition process. Conclusively, sludge treatment wetlands can be successfully used, not only to dewater, but also to stabilize and mature wastewater sludge after approximately a four-month resting phase.